A conventional battery pack for a battery powered electrical device incorporates a plurality of battery modules which are always connected in series. The battery pack has an output terminal to output a total voltage of the battery modules connected in series to the outside of the battery pack. When the battery pack is attached to a device's main body, the battery pack supplies electric power for the device's main body through the output terminal, and drives the device's main body.
When the voltage outputted from the output terminal is on the order of 10V, there are few problems, but when the voltage is on the order of 100V, an electric shock may occur if a body touches the output terminal, or smoking or ignition may occur if a piece of metal touches the output terminal.